Paper No. 2
Presentation Time: 8:20 AM
FITFUL RIFTING, GLACIATION, AND THE BIRTH OF THE CORDILLERAN MIOGEOCLINE: A NEOPROTEROZOIC-CAMBRIAN DETRITAL ZIRCON RECORD FROM NORTHERN UTAH AND SOUTHERN IDAHO
BALGORD, Elizabeth, Geology, University of Arizona, 242 E 5th St, Tucson, AZ 85705, DEHLER, Carol M., Department of Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505, YONKEE, Adolph, Department of Geosciences, Weber State University, 2507 University Circle, Ogden, UT 84408, LINK, Paul Karl, Department of Geosciences, Idaho State Univ, ISU Campus Box 8072, Pocatello, ID 83209, HAYES, Dawn S., Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84321, KEELEY, Joshua A., Department of Geosciences, Idaho State University, 619 N. Arthur, Pocatello, ID 83204, OSTERHOUT, Shannon L., Idaho State University, Pocatello, ID 83204 and RICHEY, Dave, Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84322-4505, balgord@email.arizona.edu
U-Pb detrital zircon studies on Neoproterozoic to Cambrian strata in southern Idaho and Utah indicate a dynamically changing landscape starting with development of intracratonic basins (~750 Ma), followed by early rifting and glacial episodes (~710 to 680 Ma), and culminating in the rift-drift transition to the Cordilleran miogeocline (~600 to 550 Ma). The ~750 Ma Uinta Mountain Group accumulated in an E-W basin and reflects two provenance signatures: a dominantly Archean age population derived from the proximal Wyoming craton; and a mixed age population that includes Grenville, Paleoproterozoic, and Archean grains, reflecting mixed Laurentian sources.
Diamictite-bearing strata comprise a regionally extensive N-S trending belt that records onset of regional rifting and two episodes of glaciation. A lower diamictite interval has a dominant population of Grenvillian grains. The upper diamictite interval has dominant Archean or Paleoproterozoic populations. The upper diamictite is interlayered with mafic igneous rocks that have geochemical signatures typical of continental rifting, contain trachytic volcanic clasts, and include a distinct population of ca. 680 Ma igneous zircon grains broadly synchronous with rifting and glaciation.
Detrital zircons in the overlying <665 Ma to Lower Cambrian Brigham Group,which comprises a regionally extensive prism of siliciclastic strata, show mixed Laurentian provenance at the base (Grenvillian, A-type granite, Yavapai-Mojave-Mazatzal (YMM) and Neoarchean grain populations). YMM populations become more prevalent upward. Upper Brigham Group strata contain unimodal Paleoproterozoic detrital zircon peaks indicating a change to proximal sources on the uplifted rift shoulder, just prior to the rift-drift transition of the Cordilleran miogeocline. Grenville grains disappear as transcontinental drainages were flooded by the Sauk I transgression.
